1. Technical Field
The invention relates to a lens assembly equipped with a lens for forming an image using subject light on an imaging device and to an imaging apparatus having the lens assembly.
2. Description of the Related Art
Recently, cameras become mounted in vehicles. Cameras provided in vehicles are used as surveillance cameras or as driving-assistance cameras. Since display screens have been provided on driver's seats as navigation systems have become popular, the latter case is intended to display an image taken by the camera on the display screen.
In such on-board cameras, most of those are required to have waterproof performance since those are mainly used outside of vehicles. In order to achieve sufficient waterproof performance without an increase in camera size in accordance with the requirement, it has been attempted to provide, in the on-board cameras, small-sized lens assemblies excellent in waterproof performance.
FIG. 6 is a view illustrating a section of a related-art lens assembly taken along an optical axis of a taking lens. FIG. 7 is an enlarged section view illustrating a part, in which an O-ring is disposed, of the lens assembly shown in FIG. 6.
FIG. 6 shows a lens assembly 100 including a taking lens 101_1 of a first group, a taking lens 101_2 of a second group, a taking lens 101_3 of a third group, and a taking lens 101_4 of a fourth group in order from an incident side of subject light A. Furthermore, FIG. 6 shows a lens frame 102 housing these taking lenses 101_1, 101_2, 101_3, and 101_4 and an O-ring 103 disposed between the taking lens 101_1 and the lens frame 102. Specifically, as shown in FIG. 7, the taking lens 101_1 includes an object-side outer peripheral surface 101_1a and an image-side outer peripheral surface 101_1b having a diameter smaller by one step than that of the outer peripheral surface 101_1a. On the other hand, the lens frame 102 includes an inner surface 102a. The O-ring 103 is fitted to the image-side outer peripheral surface 101_1b, and the O-ring 103 is disposed with being pressed in directions of arrows P and P′ by the outer peripheral surface 101_1b and the inner surface 102a. The O-ring 103 is a rubber member that exhibits waterproof performance after the taking lens 101_1 is housed in the lens frame 102. Also, examples of a material of the O-ring 103 include an ethylene propylene based rubber, a silicon rubber, and the like.
Also, JP 2002-90603 A (corresponding to U.S. Pat. No. 6,507,700) has proposed a lens assembly in which a protrusion of a leading end of the lens frame is caulked on the front surface side of the taking lens in the way of thermal adhesion in a state where the O-ring disposed between the outer peripheral surface of the taking lens and the inner wall surface of the lens frame is pressed.
The above-described O-ring, which is a rubber member exhibiting waterproof performance, is molded by jointing two molds. Hence, the molded O-ring has parting lines incidentally formed on a boundary part between these two molds. Protrusion shaped burrs are easily formed on the parting lines. The O-ring is disposed so that the protrusion shaped burrs are located on the outer peripheral surface side of the taking lens and on the inner surface side of the lens frame. Therefore, if the O-ring is pressed by the outer peripheral surface of the taking lens and the inner surface of the lens frame, the O-ring main body is pressed from above the protrusion shaped burrs. In this case, the protrusion shaped burrs may be embedded in the O-ring main body or the O-ring may get twisted. Accordingly, since it is hard to uniformly press the O-ring, it is hard to secure close contact between the outer peripheral surface of the taking lens and the O-ring and close contact between the inner surface of the lens frame and the O-ring. As a result, it is hard to sufficiently secure waterproof performance between the taking lens and the O-ring and waterproof performance between the lens frame and the O-ring.